The present invention relates to applications for automatic cut-off of the engine when the vehicle is stopped with restarting using the foot lever of the brake pedal and/or pressing of the accelerator pedal by the driver, referred to as “stop and start”, in vehicles which are provided with automatic or automated transmissions which are provided with a system for progressive coupling of the engine with the transmission during restarting operations.
More specifically, it relates to a method and a device for controlling the automatic restart of a vehicle which is provided with an automatic transmission when the brake pedal is released or the accelerator pedal is pressed by the driver.
In vehicles which are provided with automatic transmissions, the demands in terms of driving performance and comfort require a particularly reduced automatic “restart” time of the vehicle. This restriction involves rapidly increasing the engine torque in the restart phase in various situations of automatic stoppage of the engine during travel, and reducing, to the greatest possible extent, the time for transferring the engine torque to the wheels.
In most current “Stop and Start” applications, the “reliability” of the engine torque transmitted when starting is prioritized. To this end, there is defined a high engine speed threshold, below which the torque transfer to the transmission system is not established.
The threshold is generally similar to the establishment of the deceleration speed. This option unfortunately becomes evident as a particularly significant delay in authorization of the transmission of the torque to the wheels, which does not allow the objectives for reducing the restart time to be complied with.
The methods in which a minimum speed threshold is imposed on the engine before authorizing the transmission of the torque to the transmission in particular have the following disadvantages:                if the threshold is selected to be at the lowest level (towards the “autonomous” engine speed threshold), the engine torque available is at risk of being less than the instruction to be transmitted to the gearbox in order to prevent stalling and to be able to start as quickly as possible,        if it is selected to be at the highest level, besides the loss of time connected with the transfer delay, the time for which the torque is available at the wheels may be affected by the non-linearity of the instantaneous speed profile in accordance with time.        